This application is based on Japanese Patent Application No. 2001-242468 filed Aug. 9, 2001 and No. 2002-226654 filed Aug. 2, 2002 the content of which are incorporated hereinto by reference.
1. Field of the Invention
The present invention relates to an IC socket that functions as a contact medium between an IC package and a printed circuit board and more specifically to a technology for connecting leads of the IC package to corresponding terminals of the printed circuit board for effective evaluation of characteristics of the IC package.
2. Description of the Prior Art
As operation signal frequencies of integrated circuits have been increasing in recent years, a variety of kinds of IC sockets have been developed which have contacts with low inductance. In the IC sockets with reduced inductance and improved radio frequency characteristics, it is necessary to shorten the length of signal lines of the socket contacts as much as possible. At the same time, the contacts need to have a structure that allows them to elastically contact the leads of the IC package with some pressure. However, for contacts of a type that is formed with a spring portion when the contact is punched out of a metal plate material, the pressure contact characteristic imposes a limit on the reduction in the length of the spring portion, i.e., signal line length. It is therefore difficult with this type of contacts to achieve a required reduction in inductance.
To overcome this problem, Japanese Patent Application Laid-open No. 10-050440 (1998) (Japanese Patent Application No. 8-204994 (1996)) proposes an IC socket in which an elastic body is interposed between a socket cover and contacts, which are to contact the leads of an IC package, to hold the contacts in a standby posture and in which an elastic recovery force of the elastic body is utilized to produce a contact pressure between the contacts and the IC leads.
With the above IC socket, however, since an elastic body is interposed between the contacts and the cover and there are scattered fixing portions for fixing a socket base and the cover, the contact pressures near the fixing portions tend to become higher than those of other portions. As a result, the contact pressure produced between the contacts of the IC socket and the IC package leads are not uniform over the entire length of a row of contacts, leaving a possibility of a part of the contacts failing to contact the IC package. This poses a problem in establishing a condition for an appropriate contact pressure.
With a view to overcoming this problem experienced with conventional IC sockets, it is an object of the present invention to provide an IC socket that can realize a uniform contact pressure between the contacts and the IC package over the entire contacts, thus allowing an appropriate evaluation of characteristics of an IC package being tested.
To solve the problem described above, an IC socket of the present invention mounted on a printed circuit board comprises: a socket base having a large number of contacts arranged in a row and brought into contact with leads of an IC package; a cover bearing on the contacts through an elastic body; and fixing portions for securing the cover to the socket base; wherein a contact surface between the elastic body and the contacts is curved in a longitudinal direction and the curved surface is so shaped as to generate a uniform contact force between the contacts and the leads of the IC package.
The curved surface may be formed according to a predetermined contact force distribution curve.
Further, the contact force distribution curve can be obtained by simultaneously displacing all of a number of contacts arranged in a row a predetermined distance and measuring a contact force of each contact successively.
The contact surface of the cover with the elastic body may be formed into the shape of the curved surface.
The elastic body may have its contact surface with the cover formed planar and its contact surface with the contacts formed into the shape of the curved surface.
The elastic body may be rubber.
Further, the elastic body may be a hollow tube.
Here, the contacts each have a first contact portion protruding inwardly of the IC socket and adapted to contact one of the leads of the IC package; a second contact portion pivotally supporting the contact and adapted to contact one of interconnect lines on the printed circuit board; and a pressure portion adapted to press the elastic body as the contact is pivoted.
The first contact portion, the second contact portion and the pressure portion may be integrally formed.
With this invention, a non-uniform pressing force that varies in magnitude depending on the positions of the fixing portions and which is applied to the contacts through the elastic body can be eliminated by shaping the socket cover in conformity with the contact force distribution curve. It is thus possible to provide an IC socket capable of producing a uniform pressing force in the contacts and thereby enable an appropriate evaluation of characteristics of the IC package.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.